Microstructural characteristics and protection performances of plasma-sprayed Al2O3–Al composite coatings on AZ91D magnesium alloy

Four Al2O3-Al composite coatings were successfully fabricated on AZ91D alloy by plasma sprayed with changing ratios of Al2O3 and Al mixed powders, respectively. XRD results indicate that all the composite coatings are composed of γ-Al2O3, α-Al2O3, and Al. SEM and EDS analysis find that Al2O3-Al composite coatings present the interlaced structures of Al and Al2O3 bands. VIDAS image analysis reveals that the porosities of the composite coatings are increased by adding Al2O3. In the composite coatings, the hardness of Al is about 62 HV and that of Al2O3 is up to 1380 HV. The electrochemical polarization tests testify that Al2O3-Al composite coatings can effectively protect AZ91D alloy from corroding in a chloride environment. The wear test results confirm that the wear resistance of Al2O3-Al composite coatings is markedly superior to that of AZ91D alloy. The excellent protection degrees are attributed to their particular compositions, microstructures, and properties. Moreover, the effect of Al2O3 contents on the microstructures and protection performances of Al2O3-Al composite coatings was also studied and discussed in detail